Fix systemd example configuration

Closes gh-42795

Author: mhalbritter

spring-boot-project/spring-boot-docs/src/docs/asciidoc/deployment/installing.adoc

@@ -22,17 +22,16 @@ The following script offers an example:
 	User=myapp
 	Group=myapp
 
-	Environment="JAVA_HOME=/path/to/java/home"
-
-	ExecStart=${JAVA_HOME}/bin/java -jar /var/myapp/myapp.jar
-	ExecStop=/bin/kill -15 $MAINPID
+    Type=exec
+	ExecStart=/path/to/java/home/bin/java -jar /var/myapp/myapp.jar
+    WorkingDirectory=/var/myapp
 	SuccessExitStatus=143
 
 	[Install]
 	WantedBy=multi-user.target
 ----
 
-IMPORTANT: Remember to change the `Description`, `User`, `Group`, `Environment` and `ExecStart` fields for your application.
+IMPORTANT: Remember to change the `Description`, `User`, `Group`, `ExecStart` and `WorkingDirectory` fields for your application.
 
 NOTE: The `ExecStart` field does not declare the script action command, which means that the `run` command is used by default.